1. Field of the Invention
The present invention relates to a technology for performing data input/output with respect to a recording medium by detecting a servo sync mark used for positioning of a head.
2. Description of the Related Art
In a storage apparatus that performs data input/output with respect to a disk-shaped (circular) recording medium, such as a hard disk device, a plurality of tracks are formed on the recording medium at the time of initialization, and servo sync marks serving as marks for data access on respective tracks are written at equal intervals. A data access to a desired data position is performed by detecting positions of the servo sync marks.
Because the servo sync marks are used as references for the data access, it is important to make writing intervals of the servo sync marks equal for improvement of a format efficiency and improvement of a success rate of the data access. However, even when servo sync marks intervals are calculated from the number of servo sync marks to be written on an identical track and a circumference of the track and the servo sync marks are written according to the calculated servo sync mark intervals, an interval between the servo sync mark written first and the servo sync mark written last (hereinafter, “link interval”) largely deviates from other servo sync mark intervals. This is because deviation of the servo sync mark intervals due to unevenness of rotation of the recording medium is accumulated while the servo sync marks are written on the entire track.
A technology for suppressing such deviation of the link intervals by improving writing accuracy of the servo sync marks is proposed in Japanese Patent Application Laid-Open No. 2004-199770. This technology provides a second head for writing a reference clock separately from a head for writing servo sync marks and writing the servo sync marks based on the reference clock written by the second head.
Japanese Patent Application Laid-Open No. 2002-133771 discloses a disk synchronous write (DSW) system for improving a success rate of data access by correcting data access timing based on measured servo sync mark intervals, by assuming that servo sync mark intervals are unequal.
However, in the technology disclosed in Japanese Patent Application Laid-Open No. 2004-199770, it is necessary to provide the two heads in a storage apparatus. This is disadvantageous in terms of manufacturing cost and a size compared with a normal storage apparatus having one head. When a recording medium having the servo sync marks is built in a storage apparatus at the time of manufacturing, it is impossible to apply this technology. This is because, even when servo sync marks are equally written, reading intervals of the servo sync marks are not equal because of an influence of eccentricity of the recording medium.
Therefore, it is conceivable to eliminate the influence of eccentricity of the recording medium using the technology disclosed in Japanese Patent Application Laid-Open No. 2002-133771. However, the data access timing is corrected excessively because of an influence of deviation of the link intervals from an ideal interval (hereinafter, “link amount”). Therefore, a recording capacity of the recording medium decreases because of necessity for performing format processing taking into account the link amount. In the storage apparatus including the recording medium having the servo sync marks recorded in advance, a data access error tends to occur when the link amount exceeds a tolerance.
Therefore, it is desirable to realize a storage apparatus that can keep a sufficient recording capacity and can prevent occurrence of a data access error even when intervals of servo sync marks recorded in a recording medium are not equal and, in particular, when the link interval is present.